MOSCOW, September 14. /TASS/. Russia’s law enforcement authorities are still trying to track down those responsible for a string of bomb threat calls in Russian cities, including Moscow, but at this point it is already clear it was a well-orchestrated attack, a source in the law enforcement has told TASS.

"The perpetrators have not been identified yet. Investigative and detective work is in progress. All threat calls were made via messengers, but practically all outgoing messages had different IP-addresses. It is possible that the telephones had VPN connections," the source said.

"At this point it is known that it was a well-orchestrated campaign staged by one group of persons or even one person, in different Russian cities, including Moscow," the source said.

"Checks are being made if some extremist organizations might be responsible," he said adding that no other conclusions could be made at this point. According to the official most messages were addressed to trade centers, schools and so on and so forth.

"All callers were speaking Russian without any accent. None of the threats proved real," the source said.

He confirmed that a criminal investigation was underway in Moscow over the numerous false phone bomb threats that were received on Wednesday.

"This is a multiple case. It was opened under article 207 of the Criminal Code (False Terrorist Act Threat). Similar criminal cases are being investigated in other cities," law enforcement agencies said.